Here it is:
http://alancordwell.co.uk/Legacy/radionavigation/hifix/soundclips.html
scroll down to 'Other hyperbolic systems' : BRAS
BRAS
Now as it happened, David Sparvell G4FTC pointed out to me that there are some
sort of transmissions audible on 1810 kHz after dark. David and myself did some
work on this signal; we think it's a hyperbolic system very similar in
characteristics to HiFix but with some subtle differences- for example, the
transmissions are simultaneously on 2 frequencies 815 Hz apart- which could be
for lane identification. You can hear two sites quite well with differing fading
patterns indicating significantly diffrent locations; and a third can just be
heard when the signal is on a peak.
We speculated about the source, as Russia seemed a good bet on two counts- it
explains the signal coming up after dark, and its possible they still use MF
hyperbolic systems.
I did some trawling on the web and came up with these:
"...there are Russian BRAS and RS-10 navigation systems spreading all over the
topband. They sound like a series of dashes.
As these signals are used for hydrographic purposes, they are more active during
summer time."
- Vaino Lehtoranta, OH2LX writing on October 1998 on the top band contesting
message board. And, from the Spooks Newsletter, another quote from Vaino:
>“...frequency is 3756 kHz with much reduced carrier. It is modulated by tone
>which spreads up and down symmetrically in about 0.82 kHz steps. Because this
>is exactly what Bras and Rs-10 transmit, these must have something to do with
>those systems. A control station? Some people long thought they are time signal
>stations without knowledge that the transmitted “time period” is not 1
>second....”Interesting.
Anyway here's the sound clip- This is the 'beat' between the two of the 820 Hz
sidebands, which is resolved on an AM receiver.
That corresponds to what I see on my Topband waterfall SDR, see picture sent in
my earlier message.
There is also a sound example:
http://alancordwell.co.uk/Legacy/radionavigation/hifix/sounds/1810kHz_AM.mp3
73
Mark PA5MW
> Op 20 februari 2018 om 8:14 schreef Mark van Wijk <pa5mw@home.nl>:
>
> I also read somewhere these are navigation beacons in North East-sea area.
> Anyone have a known explaining source for this?
>
> Their transmission consist of three T's; where the 3rd one is 20dB lower in
> output and can only be hrd when they are very loud.
>
> About 21 of these can be hrd on 160m, where indeed at about 1813 it seems the
> loudest.
>
> For an example see:
> https://www.flickr.com/photos/pa5mw/38528517942/in/album-72157688739777191/
>
> 73
>
> Mark PA5MW
>
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